Morphophysiological study of digestive system litter-feeding termite Cornitermes cumulans (Kollar, 1832).

Termites are the major decomposers of lignocellulosic biomass on Earth and are commonly considered as biological reactor models for lignocellulose degradation. Despite their biotechnological potential, few studies have focused on the morphophysiological aspects of the termite digestive system. We therefore analyze the morphology, ultrastructure and gut luminal pH of the digestive system in workers of the litter-feeding termite Cornitermes cumulans (Blattodea: Termitidae). Their digestive system is composed of salivary glands and an alimentary canal with a pH ranging from neutral to alkaline. The salivary glands have an acinar structure and present cells with secretory characteristics. The alimentary canal is differentiated into the foregut, midgut, mixed segment and hindgut, which comprises the ileum (p1), enteric valve (p2), paunch (p3), colon (p4) and rectum (p5) segments. The foregut has a well-developed chewing system. The midgut possesses a tubular peritrophic membrane and two cell types: digestive cells with secretory and absorptive features and several regenerative cells in mitosis, both cell types being organized into regenerative crypts. The mixed segment exhibits cells rich in glycogen granules. Hindgut p1, p4 and p5 segments have flattened cells with a few apical invaginations related to mitochondria and a thick cuticular lining. Conversely, the hindgut p3 segment contains large cuboid cells with extensive apical invaginations associated with numerous mitochondria. These new insights into the morphophysiology of the digestive system of C. cumulans reveal that it mobilizes lignocellulose components as a nutritional source by means of a highly compartmentalized organization with specialized segments and complex microenvironments.

Midgut morphophysiology in Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae).

Sitophilus zeamais is one of the most aggressive pests of stored grains, causing a significant decrease in the nutritional quality of the grains and major losses in economic trade. The foraging capacity of this pest is assigned to its highly efficient digestive system. Investigations on the morphofunctional features of the midgut, which is the most active region of the alimentary canal, are fundamental to understand the feeding habits of this species. In this study, the midgut of adult insects was isolated, processed, and analyzed on light microscopy, scanning and transmission electron microscopy, protein and enzymatic activities determination, including analyses of the starch hydrolysis products. In S. zeamais, the midgut was differentiated into anterior midgut and posterior midgut, and consisted of digestive, regenerative and endocrine cells. The anterior midgut showed high density of regenerative crypts. Cells containing organelles associated with protein synthesis and presence of amylases and lipases indicated that majority of the digestion process occurred in the anterior midgut. The posterior midgut exhibited numerous gastric caeca and peritrophic membrane. Cells with poorly differentiated cytoplasmic into organelles, elongated microvilli, and low enzymatic activities indicated that the posterior midgut was mainly involved in absorption.